Data storage media containing transparent polycarbonate blends

ABSTRACT

The invention relates to transparent blends of polymers suitable for use in optical articles; the polymers contain residues of BCC and its derivatives, and have properties particularly suited for use in high density optical data storage media. The polymers further contain residues of other polymers, such as α-methyl polystyrene and polystyrene derivatives; bisphenols, such as bisphenol A; cycloaliphatic polyester resins, such as PCCD and its derivatives or some combination of each.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 09/858,582,filed May 17, 2001 now U.S. Pat. No. 6,593,425, which claims priorityfrom Provisional application Ser. No. 60/294,202 filed May 31, 2000which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

This invention relates to transparent miscible blends of polymerssuitable for use in optical articles. This invention further relates tooptical articles, and methods for making optical articles from thetransparent blends.

In addition to use as optical articles, the blends of the invention areuseful in producing transparent articles of manufacture having goodproperties. These properties include food chemical resistance and meltprocessibility. These blends are especially useful for makingtransparent molded articles, fibers, films and sheeting.

Polycarbonates and other polymer materials are utilized in optical datastorage media, such as compact disks. In optical data storage media, itis critical that polycarbonate resins have good performancecharacteristics such as transparency, low water affinity, goodprocessibility, good heat resistance, and low birefringence. Highbirefringence is particularly undesirable in high density optical datastorage media.

Improvements in optical data storage media, including increased datastorage density, are highly desirable, and achievement of suchimprovements is expected to improve well established and new computertechnology such as read only, write once, rewritable, digital versatile,and magneto-optical (MO) disks.

In the case of CD-ROM technology, the information to be read isimprinted directly into a moldable, transparent plastic material, suchas bisphenol A (BPA) polycarbonate. The information is stored in theform of shallow pits embossed in a polymer surface. The surface issputtered with a reflective metallic film, and the digital information,represented by the position and length of the pits, is read opticallywith a focused low power (5 mW) laser beam.

The operating principle in a write once read many (WORM) drive is to usea focused laser beam (20-40 mW) to make a permanent mark on a thin filmon a disk. The information is then read out as a change in the opticalproperties of the disk, e.g., reflectivity or absorbance.

Although the CD-ROM and WORM formats have been successfully developedand are well suited for particular applications, the computer industryis focusing on erasable media for optical storage (EODs). There are twotypes of EODs: phase change (PC) and magneto-optic (MO). In MO storage,a bit of information is stored as a ˜1 μm diameter magnetic domain,which has its magnetization either up or down. The information can beread by monitoring the rotation of the plane polarization of lightreflected from the surface of the magnetic film. This rotation, calledthe Magneto-Optic Kerr Effect (MOKE) is typically less than 0.5 degrees.The materials for MO storage are generally amorphous alloys of the rareearth and transition metals.

Amorphous materials have a distinct advantage in MO storage as they donot suffer from “grain noise”, spurious variations in the plane ofpolarization of reflected light caused by randomness in the orientationof grains in a polycrystalline film. Bits are written by heating abovethe Curie point, T_(c), and cooling in the presence of a magnetic field,a process known as thermomagnetic writing. In the phase-change material,information is stored in regions that are different phases, typicallyamorphous and crystalline. These films are usually alloys or compoundsof tellurium which can be quenched into the amorphous state by meltingand rapidly cooling. The film is initially crystallized by heating itabove the crystallization temperature. In most of these materials, thecrystallization temperature is close to the glass transitiontemperature. When the film is heated with a short, high power focusedlaser pulse, the film can be melted and quenched to the amorphous state.The amorphized spot can represent a digital “1” or a bit of information.The information is read by scanning it with the same laser, set at alower power, and monitoring the reflectivity.

In the case of WORM and EOD technology, the recording layer is separatedfrom the environment by a transparent, non-interfering shielding layer.Materials selected for such “read through” optical data storageapplications must have outstanding physical properties, such asmoldability, ductility, a level of robustness compatible with popularuse, resistance to deformation when exposed to high heat or highhumidity, either alone or in combination. The materials should alsointerfere minimally with the passage of laser light through the mediumwhen information is being retrieved from or added to the storage device.

As data storage densities are increased in optical data storage media toaccommodate newer technologies, such as digital versatile disks (DVD),recordable and rewritable digital versatile disks (DVD-R and DVD-RW),high density digital versatile disks (HD-DVD), digital video recorders(DVR), and higher density data disks for short or long term dataarchives, the design requirements for the transparent plastic componentof the optical data storage devices have become increasingly stringent.In many of these applications, previously employed polycarbonatematerials, such as BPA polycarbonate materials, are inadequate.Materials displaying lower birefringence at current, and in the futureprogressively shorter “reading and writing” wavelengths have been theobject of intense efforts in the field of optical data storage devices.

Low birefringence alone will not satisfy all of the design requirementsfor the use of a material in optical data storage media; hightransparency, heat resistance, low water absorption, ductility, highpurity and few inhomogeneities or particulates are also required.Currently employed materials are found to be lacking in one or more ofthese characteristics, and new materials are required in order toachieve higher data storage densities in optical data storage media. Inaddition, new materials possessing improved optical properties areanticipated to be of general utility in the production of other opticalarticles, such as lenses, gratings, beam splitters and the like.

In applications requiring higher storage density, the properties of lowbirefringence and low water absorption in the polymer material fromwhich the optical article is fabricated become even more critical. Inorder to achieve higher data storage density, low birefringence isnecessary so as to minimally interfere with the laser beam as it passesthrough the optical article, for example a compact disk.

Another critical property needed for high data storage densityapplications is disk flatness. The disk flatness is dependent upon theflatness of the polycarbonate substrate immediately after the injectionmolding process as well as the dimensional stability of the substrateupon exposure to high humidity environments. It is known that excessivemoisture absorption results in disk skewing which in turn leads toreduced reliability. Since the bulk of the disk is comprised of thepolymer material, the flatness of the disk depends on the low watersolubility and low rate of water diffusion into the polymeric material.In addition, the polymer should be easily processed in order to producthigh quality disks through injection molding.

There exists a need for compositions having good optical properties andgood processibility and which are suitable for use in high densityoptical recording media. Polycarbonates manufactured by copolymerizingthe aforementioned aromatic dihydroxy compounds, such as BPA, with othermonomers, such as 6,6′-dihydroxy-3,3,3′,3′-tetramethylspirobiindane(SBI), may produce acceptable birefringence; however the glasstransition temperature (T_(g)) melt viscosity is often too high,resulting in poor processing characteristics. Consequently, the obtainedmoldings have low impact resistance and low pit replication. Further,the water absorption of such polycarbonates is unacceptable for higherdensity applications.

BRIEF SUMMARY OF THE INVENTION

The present invention solves these problems, and provides compositionsfor storage media having unexpected and advantageous properties. Theseand further objects of the invention will be more readily appreciated byconsidering the following disclosure and appended claims.

The present invention, in one aspect, relates to the blending ofpolymers to produce transparent miscible blend compositions. In afurther aspect, the applicants were surprised to discover that thetransparent miscible blend compositions of the present invention possesssuitable properties for use in optical articles, in particular for usein optical data storage media.

The present invention relates to transparent blends of polymers suitablefor use in optical articles; the polymers contain residues of BCC andits derivatives, and have properties particularly suited for use in highdensity optical data storage media. The polymers further containresidues of other polymers, such as α-methyl polystyrene and polystyrenederivatives; bisphenols, such as bisphenol A; cycloaliphatic polyesterresins, such as PCCD and its derivatives or some combination of each.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to thefollowing detailed description of preferred embodiments of the inventionand the Examples included therein.

Before the present compositions of matter and methods are disclosed, itis to be understood that this invention is not limited to specificsynthetic methods or to particular formulations, as such may, of course,vary. It is also to be understood that the terminology used herein isfor the purpose of describing particular embodiments only and is notintended to be limiting.

In this specification and in the claims which follow, reference will bemade to a number of terms which shall be defined to have the followingmeanings.

The singular forms “a,” “an” and “the” include plural referents unlessthe context transparently dictates otherwise.

The term “miscible” refers to blends that are a mixture on a molecularlevel wherein intimate polymer-polymer interaction is achieved.

The term “transparent” is defined herein as an absence of cloudiness,haziness, and muddiness when inspected visually. Transparency wasdetermined by measuring transmission, haze, and yellowness index (YI)using a Gardner Colorimeter.

“Optional” or “optionally” means that the subsequently described eventor circumstances may or may not occur, and that description includesinstances where the event or circumstance occurs and instances where itdoes not.

“BCC” is herein defined as 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane.

“BisAP” is herein defined as1,1-bis(4-hydroxyphenyl)methylphenylmethane.

“AMPS” is herein defined as α-methyl polystyrene.

“PS” is herein defined as polystyrene.

“PCCD” is herein defined as poly(cyclohexane-1,4-dimethylenecyclohexane-1,4-dicarboxylate).

“Polycarbonate” or “polycarbonates” as used herein includescopolycarbonates, homopolycarbonates and (co)polyester carbonates.

“C_(g)” is the stress optical coefficient of a polymeric material in theglassy state, measured in Brewsters (10⁻¹³ cm²/dyne).

“IBR” is the in-plane birefringence of the molded article, measured inunits of nanometers.

“VBR” is the vertical birefringence of the molded article, measured inunits of nanometers per millimeter (nm/mm).

“Optical articles” as used herein includes optical disks and opticaldata storage media. For example, a compact disk (CD audio or CD-ROM), adigital versatile disk, also known as DVD (ROM, RAM, rewritable), arecordable digital versatile disk (DVD-R), a digital video recording(DVR), a magneto optical (MO) disk and the like; optical lenses, such ascontact lenses, lenses for glasses, lenses for telescopes, and prisms;optical fibers; information recording media; information transferringmedia; high density data storage media, disks for video cameras, disksfor still cameras and the like; as well as the substrate onto whichoptical recording material is applied. In addition to use as a materialto prepare optical articles, a blend of the present invention may beused as a raw material for films or sheets.

“Optical data storage media” of the present invention may be of anytype, with compact disks (CDs), digital versatile disks (DVDs), DVD-RWs,HD-DVDs, DVD-Rs, DVRs, and magneto optical disks (MO) being mostpreferred. Devices may also include recordable and rewritable opticaldata storage media. In one embodiment of the device, a reflective metallayer is attached directly to the substrate comprising the transparentmiscible blend, where the metal layer comprises aluminum, gold, silver,or alloys thereof.

Unless otherwise stated, “mole %” in reference to the composition of apolycarbonate in this specification is based upon 100 mole % of therepeating units of the polycarbonate. For instance, “a polymercomprising 90 mole % of BCC” refers to a polycarbonate in which 90 mole% of the repeating units are residues derived from BCC diphenol or itscorresponding derivative(s). Corresponding derivatives include but arenot limited to, corresponding oligomers of the diphenols; correspondingesters of the diphenol and their oligomers; and the correspondingchloroformates of the diphenol and their oligomers.

The terms “residues” and “structural units”, used in reference to theconstituents of the polymers, are synonymous throughout thespecification.

Throughout this application where publications are referenced, thedisclosures of these publications in their entireties are herebyincorporated by reference into this application in order to more fullydescribe the state of the art to which this invention pertains.

In one aspect, this invention relates to transparent miscible blendcompositions, the transparent miscible blend composition comprising twopolymers, wherein said polymers are selected from the group comprisingA, B, and C, wherein

(A) is a polycarbonate comprising structural units corresponding tostructure (I)

where

-   -   R₁ and R₂ independently comprise a C₁-C₆ alkyl;    -   X comprises CH₂;    -   m is an integer from 4 to 7;    -   n is an integer from 1 to 4; and    -   p is an integer from 1 to 4        with the proviso that at least one of R₁ or R₂ is in the 3 or 3′        position;

(B) is a polymer comprising structural units corresponding to structure(II)

where R₃ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy; and

(C) is a polymer comprising structural units corresponding to structure(III)

where R₄, R₅ and R₆ independently comprise a C₁-C₆ alkyl.

In another aspect, this invention relates to transparent miscible blendcompositions, the transparent miscible blend composition comprisingpolymers A and D, wherein

(A) is a polycarbonate comprising structural units corresponding tostructure (I)

where

-   -   R₁ and R₂ independently comprise a C₁-C₆ alkyl;    -   X comprises CH₂;    -   m is an integer from 4 to 7;    -   n is an integer from 1 to 4; and    -   p is an integer from 1 to 4        with the proviso that at least one of R₁ or R₂ is in the 3 or 3′        position; and

(D) is a cycloaliphatic polyester resin comprising structural unitscorresponding to structure (IV)

wherein R₇ comprises a residue of an aryl, alkane or cycloalkanecontaining diol having from 6 to 20 carbon atoms and R₈ comprises adecarboxylated residue of an aryl, aliphatic or cycloalkane containingdiacid having form 6 to 20 carbon atoms with the proviso that at leastone of R₇ or R₈ is cycloaliphatic.

In a further aspect, the invention relates to transparent miscible blendcompositions, the transparent miscible blend composition comprisingpolymers A, B, and C, wherein

(A) is a polycarbonate comprising structural units corresponding tostructure (I)

where

-   -   R₁ and R₂ independently comprise a C₁-C₆ alkyl;    -   X comprises CH₂;    -   m is an integer from 4 to 7;    -   n is an integer from 1 to 4; and    -   p is an integer from 1 to 4        with the proviso that at least one of R₁ or R₂ is in the 3 or 3′        position;

(B) is a polymer comprising structural units corresponding to structure(II)

where R₃ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy, and

(C) is a polymer comprising structural units corresponding to structure(III)

where R₄, R₅ and R₆ independently comprise a C₁-C₆ alkyl.

In a further aspect, the invention relates to transparent miscible blendcompositions, the transparent miscible blend composition comprisingpolymers A, B, and E, wherein

(A) is a polycarbonate comprising structural units corresponding tostructure (I)

where

-   -   R₁ and R₂ independently comprise a C₁-C₆ alkyl;    -   X comprises CH₂;    -   m is an integer from 4 to 7;    -   n is an integer from 1 to 4; and    -   p is an integer from 1 to 4        with the proviso that at least one of R₁ or R₂ is in the 3 or 3′        position;

(B) is a polymer comprising structural units corresponding to structure(II)

where R₃ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy, and

(E) is a polymer comprising structural units corresponding to structure(V)

where R₉ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy.

In a further aspect, the invention relates to transparent miscible blendcompositions, the transparent miscible blend composition comprisingpolymers B, C, and E, wherein

(B) is a polymer comprising structural units corresponding to structure(II)

where R₃ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy,

(C) is a polymer comprising structural units corresponding to structure(III)

where R₄, R₅ and R₆ independently comprise a C₁-C₆ alkyl, and

(E) is a polymer comprising structural units corresponding to structure(V)

where R₉ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy.

Transparent miscible blends of polymers are rare. Transparent miscibleblends are not translucent or opaque. Differential scanning calorimetrytesting detects only a single glass transition temperature (T_(g)) formiscible blends composed of two or more components. In addition,scanning electron microscopy detects no contrast indicative ofimmiscible phases.

Birefringence in an article molded from polymeric material is related toorientation and deformation of its constituent polymer chains.Birefringence has several sources, including the structure and physicalproperties of the polymer material, the degree of molecular orientationin the polymer material, and thermal stresses in the processed polymermaterial. For example, the birefringence of a molded optical article isdetermined, in part, by the molecular structure of its constituentpolymer and the processing conditions, such as the forces applied duringmold filling and cooling, used in its fabrication which may createthermal stresses and orientation of the polymer chains.

The observed birefringence of a disk is therefore determined by themolecular structure, which determines the intrinsic birefringence, andthe processing conditions, which may create thermal stresses andorientation of the polymer chains. Specifically, the observedbirefringence is typically a function of the intrinsic birefringence andthe birefringence introduced upon molding articles, such as opticaldisks. The observed birefringence of an optical disk is typicallyquantified using a measurement termed “in-plane birefringence” or IBR,which is described more fully below.

For a molded optical disk, the IBR is defined as:IBR=(n _(r) −n _(θ))d=Δn _(rθ) d  (3)where n_(r) and n_(θ) are the refractive indices along the r and θcylindrical axes of the disk; n_(r) is the index of refraction seen by alight beam polarized along the radial direction; n_(θ) is the index ofrefraction for light polarized azimuthally to the plane of the disk; andd is a measure of the thickness of the disk. The IBR governs thedefocusing margin, and a reduction of IBR will lead to the alleviationof problems that are not mechanically correctable. IBR, formally calleda retardation, is a property of the finished optical disk, and has unitsof nanometers.

Two useful gauges of the suitability of a material for use as a moldedoptical article, such as a molded optical data storage disk, are thematerial's stress optical coefficient in the melt (C_(m)) and its stressoptical coefficient in the glassy state (C_(g)), respectively. Therelationship between C_(m), C_(g) and birefringence may be expressed asfollows:Δn=C _(m)×Δσ_(m)  (1)Δn=C _(g)×Δσ_(g)  (2)where Δn is the measured birefringence and Δσ_(m) and Δσ_(g) are theapplied stresses in the melt and glassy states, respectively. The stressoptical coefficients C_(m) and C_(g) are a measure of the susceptibilityof a material to birefringence induced as a result of orientation anddeformation occurring during mold filling and stresses generated as themolded article cools.

The stress optical coefficients C_(m) and C_(g) are useful as generalmaterial screening tools and may also be used to predict the verticalbirefringence (VBR) of a molded article, a quantity critical to thesuccessful use of a given material in a molded optical article. For amolded optical disk, the VBR is defined as:

 VBR=(n _(r) −n _(z))=Δn _(rz)  (3)

where n_(r) and n_(z) are the refractive indices along the r an zcylindrical axes of the disk; n_(r) is the index of refraction seen by alight beam polarized along the radial direction, and n_(z) is the indexof refraction for light polarized perpendicular to the plane of thedisk. The VBR governs the defocusing margin, and reduction of VBR willlead to alleviation of problems which are not correctable mechanically.

In the search for improved materials for use in optical articles, C_(m)and C_(g) are especially useful since they require minimal amounts ofmaterial and are relatively insensitive to uncontrolled measurementparameters or sample preparation methods, whereas measurement of VBRrequires significantly larger amounts of material and is dependent uponthe molding conditions. In general, it has been found that materialspossessing low values of C_(g) and C_(m) show enhanced performancecharacteristics, for example VBR, in optical data storage applicationsrelative to materials having higher values of C_(g) and C_(m).Therefore, in efforts aimed at developing improved optical quality,widespread use of C_(g) and C_(m) measurements is made in order to rankpotential candidates for such applications and to compare them withpreviously discovered materials.

A blending process, as opposed to a copolymerization process, providescertain advantages. Advantages of the blending process include producingcompositions that are either expensive or unattainable by acopolymerization process.

The blend composition further provides polycarbonate blends having idealoptical properties and suitable glass transition temperatures (T_(g)),and which are suitable for use in optical articles. Suitable glasstransition temperatures are necessary to provide adequateprocessibility, for example, ideal molding characteristics.

The applicants have found that the transparent miscible polymer blendsas defined herein, are also suitable for use in high data storagedensity optical media. In particular, the blends of the presentinvention have good transparency, low water absorption, goodprocessibility, good thermal stability, and low birefringence.

In a further aspect, the present invention relates to data storage mediahaving both a data storage layer, and an adjacent transparent overlayerwherein the data storage layer is capable of reflecting an energy fieldincident upon said transparent overlayer prior to being incident uponsaid data layer. Specifically, this aspect of the present inventionrelates to data storage media comprising thin, about 100 microns toabout 0.6 mm, transparent overlayers of the defined miscible transparentblend compositions. As mentioned, an embodiment of a data storage mediumis a DVD. The DVD typically has two substrates, each about 120 mm inradius and about 0.6 mm thick. These substrates are bonded together tomake a double-sided optical medium. An alternative embodiment of a datastorage medium is a DVR, which typically has a polycarbonate substrate(data layer) of about 1.1 mm in thickness and an overlayer about 100microns in thickness, the two layers bonded using an adhesive material.

As discussed above, the transparent blend compositions posses suitableproperties for use in optical media, in particular optical data storageapplications. The transparent miscible blends of the present inventionhave glass transition temperatures in the range of about 100° C. toabout 185° C., more preferably in the range of about 125° C. to about165° C., and even more preferably in the range of about 130° C. to about150° C. The water absorption of the transparent miscible blendcompositions is preferably less than about 0.33%, and more preferablyless than about 0.2%, at equilibrium. The IBR values of a disk moldedfrom the transparent miscible blend compositions are about −100nanometers to about 100 nanometers, preferably about −50 nanometers toabout 50 nanometers, and even more preferably about −40 nanometers toabout 40 nanometers.

For the transparent miscible blend compositions comprising two polymers,the weight average molecular weight (Mw) of the first polymer and thesecond polymer, as determined by gel permeation chromatography relativeto polystyrene, is preferably in the range from about 10,000 to about100,000 grams per mol (g/mol), more preferably in the range from about10,000 to about 50,000 g/mol, and even more preferably in the range fromabout 12,000 to about 40,000 g/mol. The transparent miscible blendcompositions, comprising two polymers, preferably have a lighttransmittance of at least about 85%, more preferably at least about 90%.

For the transparent miscible blend compositions comprising threepolymers, the weight average molecular weight (Mw) of the first polymer,the second polymer, and the third polymer, as determined by gelpermeation chromatography relative to polystyrene, is preferably in therange from about 10,000 g/mol to about 100,000 g/mol, more preferably inthe range from about 10,000 to about 50,000 g/mol, even more preferablyin the range from about 12,000 to about 40,000 g/mol. The transparentmiscible blend compositions, comprising three polymers, preferably havea light transmittance of at least about 85%, more preferably at leastabout 90%.

The compositions of the particular blends may be varied within certainranges to achieve a suitable property profile. The blends are misciblethrough the whole range of compositions.

In the case of the blend compositions comprising two polymers, thepercentages of the polymers are about 1 to about 99 weight % of thefirst polymer portion and about 1 to about 99 weight % of the secondpolymer, with the total weight % of the first and second componentspreferably equal to about 100 weight %.

In the embodiments of the blends comprising two polymers, those of whichinclude polymer A as a first component and one of polymer B or polymer Das a second component, component polymer A is the dominant component andcomprises from about 1 to about 99 weight % of the blend, preferablyfrom about 10 to about 99 weight % of the blend, more preferably fromabout 30 to about 99 weight % of the blend, and even more preferablyfrom about 60 to about 99 weight % of the blend. In another embodiment,component polymer A comprise from about 90 to about 99 weight % of theblend. The second component, one of polymer B or polymer D, comprisesfrom about 1 to about 40 weight % of the blend, more preferably fromabout 5 to about 30 weight % of the blend, and even more preferably fromabout 10 to about 30 weight % of the blend, wherein the total weight %of the first and second components preferably equal to about 100 weight%.

In the embodiments of the blends comprising two polymers, those of whichinclude polymer C as a first component and polymer B as a secondcomponent, component polymer C is the dominant component and comprisesfrom about 1 to about 99 weight % of the blend, preferably from about 10to about 99 weight % of the blend, more preferably from about 30 toabout 99 weight % of the blend, and even more preferably from about 60to about 99 weight % of the blend. In another embodiment, polymer Ccomprise from about 90 to about 99 weight % of the blend. The secondcomponent, polymer B, comprises from about 1 to about 40 weight % of theblend, more preferably from about 5 to about 30 weight % of the blend,and even more preferably from about 10 to about 30 weight % of theblend.

In the embodiment of the blend comprising two polymers, those of whichinclude polymer A as a first component and polymer C as a secondcomponent, either component may be the dominant component. In analternative embodiment, polymer A and polymer B may be found in equalproportions.

The particular composition of the blend may be adjusted depending on anumber of factors including the end use of the blend and the desiredproperties of the blend. The composition of the blend is adjusted basedon the ratio of the components. For example, more of a component in theblend helps to maintain low water absorption and good birefringence.

Representative units of structure (I) include, but are not limited to,residues of 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane (BCC);1,1-bis(4-hydroxy-3-methylphenyl)cyclopentane;1,1-bis(4-hydroxy-3-methylphenyl)cycloheptane, and mixtures thereof.Residues of BCC are most preferred as structural units (I).

In one embodiment of the invention, the blend comprises from about 90 toabout 100 mol % of residues of BCC, structure (VI). BCC may be easilysynthesized from cyclohexanone and ortho-cresol.

A polycarbonate, comprising 100 mole % of structural units derived fromBCC, is herein referred to as “BCC homopolycarbonate”.

In the present invention, it is critical that the structural units ofstructure (I) be substituted in the 3 or 3′ position by at least one ofR₁ or R₂. It is preferable that n and p are equal to one, and that R₁and R₂ are present in the 3 and 3′ positions, respectively. R₁ and R₂are preferably a C₁-C₆ alkyl, more preferably a C₁-C₃ alkyl, and evenmore preferably CH₃.

There has been a great deal of interest in the blending ofpolycarbonates and polystyrenes in the last decade. It would bedesirable, for instance, to decrease the water absorption, raise themodulus, and decrease the stress optical coefficients of thepolycarbonate by blending in a polystyrene. BPA polycarbonate andpolystyrene, however, are immiscible. Therefore, it was surprising tofind that polymers having structure (I) were miscible with polymershaving structure (II), and that the resulting blend is suitable for usein optical articles, in particular, in optical data storage media.

Representative units of structure (II) are α-methyl polystyrene in whichthe phenyl ring may be substituted or unsubstituted. In one embodiment,the second polymer of the blend comprises about 100 mol % of residues ofα-methyl polystyrene. α-methyl polystyrene may be obtained by freeradical, anionic, or cationic polymerization of α-methylstyrene asdescribed in the literature.

Representative units of structure (m) are residues of BisAP in which thephenyl rings may be substituted or unsubstituted. In one embodiment, thesecond polymer of the blend comprises about 100 mol % of residues ofBisAP. BisAP may be obtained by the acid catalyzed condensation ofacetophenone with phenol.

The cycloaliphatic polyester resin comprises a polyester havingrepeating units of the structure (IV)

where at least one of R7 or R8 is a cycloalkyl containing radical.

The polyester is a condensation product where R7 is the residue of anaryl, alkane or cycloalkane containing diol having 6 to 20 carbon atomsor chemical equivalent thereof, and R8 is the decarboxylated residuederived from an aryl, aliphatic or cycloalkane containing diacid of 6 to20 carbon atoms or chemical equivalent thereof with the proviso that atleast one R7 or R8 is cycloaliphatic. Preferred polyesters of theinvention will have both R7 and R8 cycloaliphatic.

The present cycloaliphatic polyesters are condensation products ofaliphatic diacids, or chemical equivalents and aliphatic diols, orchemical equivalents. The present cycloaliphatic polyesters may beformed from mixtures of aliphatic diacids and aliphatic diols but mustcontain at least 50 mol % of cyclic diacid and/or cyclic diolcomponents, the remainder, if any, being linear aliphatic diacids and/ordiols. The cyclic components are necessary to impart good rigidity tothe polyester and to allow the formation of transparent blends due tofavorable interaction with the polycarbonate resin.

The polyester resins are typically obtained through the condensation orester interchange polymerization of the diol or diol equivalentcomponent with the diacid or diacid chemical equivalent component.

R7 and R8 are preferably cycloalkyl radicals independently selected fromthe following formula:

The preferred cycloaliphatic radical R8 is derived from the1,4-cyclohexyl diacids and most preferably greater than 70 mol % thereofin the form of the trans isomer. The preferred cycloaliphatic radical R7is derived from the 1,4-cyclohexyl primary diols such as 1,4-cyclohexyldimethanol, most preferably more than 70 mol % thereof in the form ofthe trans isomer.

Other diols useful in the preparation of the polyester resins of thepresent invention are straight chain, branched, or cycloaliphatic alkanediols and may contain from 2 to 12 carbon atoms. Examples of such diolsinclude but are not limited to ethylene glycol; propylene glycol, i.e.,1,2- and 1,3-propylene glycol; 2,2-dimethyl-1,3-propane diol; 2-ethyl,2-methyl, 1,3-propane diol; 1,3- and 1,5-pentane diol; dipropyleneglycol; 2-methyl-1,5-pentane diol; 1,6-hexane diol; dimethanol decalin,dimethanol bicyclo octane; 1,4-cyclohexane dimethanol and particularlyits cis- and trans-isomers; triethylene glycol; 1,10-decane diol; andmixtures of any of the foregoing. Preferably, a cycloaliphatic diol orchemical equivalent thereof and particularly 1,4-cyclohexane dimethanolor its chemical equivalents are used as the diol component.

Chemical equivalents to the diols include esters, such as dialkylesters,diaryl esters, and the like.

The diacids useful in the preparation of the aliphatic polyester resinsof the present invention are preferably cycloaliphatic diacids. This ismeant to include carboxylic acids having two carboxyl groups each ofwhich is attached to a saturated carbon. Preferred diacids are cyclo orbicyclo aliphatic acids, for example, decahydro naphthalene dicarboxylicacids, norbornene dicarboxylic acids, bicyclo octane dicarboxylic acids,1,4-cyclohexanedicarboxylic acid or chemical equivalents, and mostpreferred is trans-1,4-cyclohexanedicarboxylic acid or a chemicalequivalent. Linear dicarboxylic acids like adipic acid, azelaic acid,dicarboxyl dodecanoic acid, and succinic acid may also be useful.

Cyclohexane dicarboxylic acids and their chemical equivalents can beprepared, for example, by the hydrogenation of cycloaromatic diacids andcorresponding derivatives such as isophthalic acid, terephthalic acid,or naphthalenic acid in a suitable solvent such as water or acetic acidusing a suitable catalysts such as rhodium supported on a carrier suchas carbon or alumina. See, Friefelder et al., Journal of OrganicChemistry, 31, 3438 (1966); U.S. Pat. Nos. 2,675,390 and 4,754,064. Theymay also be prepared by the use of an inert liquid medium in which aphthalic acid is at least partially soluble under reaction conditionsand with a catalyst of palladium or ruthenium on carbon or silica. See,U.S. Pat. Nos. 2,888,484 and 3,444,237.

Typically, in the hydrogenation, two isomers are obtained in which thecarboxylic acid groups are in cis- or trans-positions. The cis- andtrans-isomers can be separated by crystallization with or without asolvent, for example, n-heptane, or by distillation. The cis-isomertends to blend better; however, the trans-isomer has higher melting andcrystallization temperatures and may be preferred. Mixtures of the cis-and trans-isomers are useful herein as well.

When the mixture of isomers or more than one diacid or diol is used, acopolyester or a mixture of two polyesters may be used as the presentcycloaliphatic polyester resin.

Chemical equivalents of these diacids include esters, alkyl esters,e.g., dialkyl esters, diaryl esters, anhydrides, salts, acid chlorides,acid bromides, and the like. The preferred chemical equivalents comprisethe dialkyl esters of the cycloaliphatic diacids, and the most favoredchemical equivalent comprises the dimethyl ester of the acid,particularly dimethyl-1,4-cyclohexane-dicarboxylate.

A preferred cycloaliphatic polyester is poly(cyclohexane-1,4-dimethylenecyclohexane-1,4-dicarboxylate) also referred to aspoly(1,4-cyclohexane-dimethanol-1,4-dicarboxylate) (PCCD) which hasrecurring units of formula II:

With reference to the previously set forth general formula, for PCCD, Ris derived from 1,4 cyclohexane dimethanol; and R1 is a cyclohexane ringderived from cyclohexanedicarboxylate or a chemical equivalent thereof.The favored PCCD has a cis/trans formula.

The polyester polymerization reaction is generally run in the melt inthe presence of a suitable catalyst such as a tetrakis (2-ethyl hexyl)titanate, in a suitable amount, typically about 50 ppm to about 200 ppmof titanium based upon the final product.

The preferred aliphatic polyesters used in the present transparentmolding compositions have a glass transition temperature (T_(g)) aboveabout 50° C., more preferably above about 80° C., and even morepreferably above about 100° C.

Also contemplated herein are the above polyesters with from about 1 toabout 50% by weight, of units derived from polymeric aliphatic acidsand/or polymeric aliphatic polyols to form copolyesters. The aliphaticpolyols include glycols, such as poly(ethylene glycol) or poly(butyleneglycol).

In the embodiments of the present invention comprising blending threepolymers to produce transparent miscible blends, a first polymer (B) isa polymer comprising structural units corresponding to structure (II).Second and third polymers are selected from the group comprising A, C,and E, wherein (A) is a polymer comprising structural unitscorresponding to structure (I), (C) is a polymer comprising structuralunits corresponding to structure (III), and (E) is a polymer comprisingstructural units corresponding to structure (V).

In one embodiment of the present invention, the transparent miscibleblend comprising polymers B, A, and C is from about 1 to about 50 weight% of the first polymer (B), from about 1 to about 80 weight % of thesecond polymer (A), and from about 1 to about 80 weight % of the thirdpolymer (C). More preferably, the blend comprises from about 5 to about25 weight % of the first polymer (B), from about 3 to about 70 weight %of the second polymer (A), and from about 20 to about 75 weight % of thethird polymer (C).

In one embodiment of the present invention, the transparent miscibleblend comprising polymers B, A, and E is from about 1 to about 30 weight% of the first polymer (B), from about 50 to about 98 weight % of thesecond polymer (A), and from about 1 to about 20 weight % of the thirdpolymer (E). More preferably, the blend comprises from about 5 to about20 weight % of the first polymer (B), from about 70 to about 90 weight %of the second polymer (A), and from about 5 to about 10 weight % of thethird polymer (E).

In one embodiment of the present invention, the transparent miscibleblend comprising polymers B, C, and E is from about 1 to about 30 weight% of the first polymer (B), from about 50 to about 98 weight % of thesecond polymer (C), and from about 1 to about 20 weight % of the thirdpolymer (E). More preferably, the blend comprises from about 5 to about20 weight % of the first polymer (B), from about 70 to about 90 weight %of the second polymer (C), and from about 5 to about 10 weight % of thethird polymer (E).

Representative units of structure (V) are residues of styrene in whichthe phenyl rings may be substituted or unsubstituted. In one embodiment,the third polymer of the blend comprises about 100 weight % of residuesof polystyrene.

The blends of the present invention may optionally be blended with anyother additives such as polymers that are miscible, in amounts that donot cause cloudiness, including but not limited to bisphenol A (BPA)polycarbonate or 2,2-bis(4-hydroxyphenyl)propane,6,6′-dihydroxy-3,3,3′,3′-tetramethylspirobiindane (SBI), dimethyl-BPA(DMBPA), tetramethyl-BPA (TMBPA), anddimethyl-1,1-bis(4-hydroxyphenyl)methylphenylmethane (DMbisAP).

The transparent miscible blends of the present invention may optionallybe blended with any conventional additives used in optical applications,including but not limited to dyestuffs, UV stabilizers, antioxidants,heat stabilizers, and mold release agents, to form an optical article.In particular, it is preferable to form a blend of the polycarbonate andadditives which aid in the processing of the blend to form the desiredoptical article. The blend may optionally comprise from about 0.0001 toabout 10% by weight of a predetermined desired additive, more preferablyfrom about 0.0001 to about 1.0% by weight of the predetermined desiredadditive.

Substances or additives which may be added to the polymers of thisinvention, include, but are not limited to, heat-resistant stabilizers,UV absorbers, mold-release agents, antistatic agents, slip agents,antiblocking agents, lubricants, anticlouding agents, coloring agents,fluorescent dyes and colorants, natural oils, synthetic oils, waxes,organic fillers, inorganic fillers, other miscible polymers, andmixtures thereof. Suitable antistatic agents includedistearylhydroxylamine, triphenyl amine, tri-n-octylphosphine oxide,triphenyl phosphine oxide, pyridine N-oxide, ethoxylated sorbitanmonolaurate, and poly(alkylene glycol) compounds.

Examples of the aforementioned heat-resistant stabilizers, include, butare not limited to, phenol stabilizers, organic thioether stabilizers,organic phosphide stabilizers, hindered amine stabilizers, epoxystabilizers and mixtures thereof. The heat-resistant stabilizer may beadded in the form of a solid or a liquid.

Examples of UV absorbers include, but are not limited to, salicylic acidUV absorbers, benzophenone UV absorbers, benzotriazole UV absorbers,cyanoacrylate UV absorbers, and mixtures thereof.

Examples of the mold-release agents include, but are not limited to,natural and synthetic paraffins, polyethylene waxes, fluorocarbons, andother hydrocarbon mold-release agents comprising; stearic acid,hydroxystearic acid, and other higher fatty acids, hydroxyfatty acids,and other fatty acid mold-release agents; stearic acid amide,ethylenebisstearoamide, and other fatty acid amides, alkylenebisfattyacid amides, and other fatty acid amide mold-release agents; stearylalcohol, cetyl alcohol, and other aliphatic alcohols, polyhydricalcohols, polyglycols, polyglycerols and other alcoholic mold releaseagents; butyl stearate, pentaerythritol tetrastearate, and other loweralcohol esters of fatty acid, polyhydric alcohol esters of fatty acid,polyglycol esters of fatty acid, and other fatty acid ester mold releaseagents; silicone oil and other silicone mold release agents, andmixtures of any of the aforementioned.

The coloring agent may be either a pigment or a dye. Inorganic coloringagents and organic coloring agents may be used separately or incombination in the invention.

Optionally, suitable carbonate redistribution catalysts may beintroduced into the blend. Suitable redistribution catalysts include awide variety of bases and Lewis acids. Illustrative examples include,amines, particularly 1,3-dimethylaminopropane, imidazole, benzimidazole,and benzotriazole, as well as other organic bases, for exampletetraalkylammonium hydroxides, such as tetramethylammonium hydroxide,usually as the pentahydrate, diethyldimethylammonium hydroxide, andtetraethylammonium hydroxide; tetraalkylammonium phenoxides, such astetramethylammonium phenoxide, usually as the monohydrate;tetraalkylammonium acetates, such as tetramethylammonium acetate;tetraalkylammonium tetraphenylborates, such as tetramethylammoniumtetraphenylborate; as well as lithium stearate, the lithium salt ofbisphenol A, the tetraethylammonium salt of bisphenol A, sodiumphenoxide, and the like. Other suitable organic bases includephosphines, for example, triphenylphosphine. A wide variety oforganometallics are suitable catalysts, including organotin compounds,such as di(n-butyl)tin oxide, di(n-octyl)tin oxide, di(n-butyl)tindibutoxide, di(n-butyl)tin dioctoate, dibutyltin, tetrabutyltin,tributyltin trifluoroacetate, tributyltin chlorophenoxide,bis[(dibutyl)(phenoxy)tin] oxide, and tributyltin hydride; as well asorganotitanium compounds, such as titanium tetra(isopropoxide), titaniumtetra(5-methylheptoxide), and titanium tetra(butoxide); as well as,zirconium tetra(isopropoxide), aluminum tri(ethoxide), aluminumtri(phenoxide), mercuric acetate, lead acetate, (diphenyl)mercury,(tetraphenyl)lead, and (tetraphenyl)silane. Also suitable are a varietyof hydrides, including sodium hydride, lithium hydride, aluminumhydride, boron trihydride, tantalum and niobium hydride, lithiumaluminum hydride, lithium borohydride, sodium borohydride,tetramethylammonium borohydride, tetra(n-butylammonium) borohydride,lithium tri(t-butoxy) aluminum hydride, and diphenylsilane; as well assimple inorganics, such as lithium hydroxide, sodium silicate, sodiumborate, silica, lithium fluoride, lithium chloride, lithium carbonate,and zinc oxide.

The desired optical article may be obtained by molding the transparentmiscible blend by injection molding, compression molding, extrusionmethods, and solution casting methods. Injection molding is thepreferred method of forming the article.

Because the blends of the present invention possess advantageousproperties such as low water absorption, good processibility, and lowbirefringence, they can be advantageously utilized to produce opticalarticles. End-use applications for the optical articles of the blends ofthe present invention comprise digital audio disks, digital versatiledisks, optical memory disks, compact disks, DVR and MO media and thelike; optical lenses, such as contact lenses, lenses for glasses, lensesfor telescopes, and prisms; optical fibers; magneto optical disks;information recording media; information transferring media; disks forvideo cameras, disks for still cameras, and the like.

The blend may function as the medium for data storage, i.e. the data maybe fixed onto or into the polymer. The blend may also function as thesubstrate onto which a data storage medium is applied. Further, somecombination of both functions may be employed in a single device.

In addition to use as optical articles, the blends of the presentinvention are useful in producing transparent articles of manufacturehaving favorable properties. These properties include food chemicalresistance and melt processibility. The blends of the present inventionare especially useful in making molded articles, fibers, films andsheeting.

The blends of the present invention can be made by methods which includethe blending of the polymers at temperatures above about 240° C.,preferably in the range of about 240° C. to about 300° C., for a timesufficient to form a transparent blend composition. Suitable methods forforming the blend include, but are not limited to, the melt method, thesolution prepared method, the dry blending method, and extrusion.

In addition to the compositions described above, the blends of thepresent invention may include at least one other modifying polymer.Suitable modifying polymers are those which form miscible blends withthe first and second polycarbonate portions. Possible modifying polymersinclude other polycarbonates, polyesters, polyamides, polystyrenes,polyurethanes, polyarylates, liquid crystalline polymers, vinyl polymersand the like, and mixtures thereof. Suitable modifying polymers may bedetermined by one of ordinary skill in the art by performing traditionalmiscibility tests with possible modifying polymers.

EXAMPLES

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how thecompositions of matter and methods claimed herein are made andevaluated, and not intended to limit the scope of what the inventorsregard as their invention. Efforts have been made to insure accuracywith respect to numbers (e.g., amounts, temperatures, etc.) but someerror and deviations should be accounted for. Unless indicatedotherwise, parts are by weight, temperature is in ° C. or is at roomtemperature, and pressure is at or near atmospheric.

The materials and testing procedures used for the results shown hereinare as follows:

Water absorption (% H₂O) was determined by the following method, whichis similar to ASTM D570, but modified to account for the variablethickness of the parts described in the examples. The plastic part ordisk was dried in a vacuum for over 1 week. The sample was removedperiodically and weighed to determine if it was dry (stopped loosingmass). The sample was removed from the oven, allowed to equilibrate toroom temperature in a dessicator, and the dry weight was recorded. Thesample was immersed in a water bath at 23° C. The sample was removedperiodically from the bath, the surface was blotted dry, and the weightrecorded. The sample was repeatedly immersed and the weight measureduntil the sample became substantially saturated. The sample wasconsidered substantially saturated or at “equilibrium” when the increasein weight in a 2 week period averaged less than 1% of the total increasein weight (as described in ASTM method D-570-98 section 7.4).

Glass transition temperature (T_(g)) values were determined bydifferential scanning calorimetry using a PERKIN ELMER DSC7. The T_(g)was calculated based on the ½ Cp method using a heating ramp of 20°C./minute.

Transmission measurements were obtained at 630 nm using an HP 8453UV-vis spectrophotometer. The values were not corrected for reflectionat the surface of the parts or for light scattering through thethickness of the parts. Transmission, YI and haze measurements usingvisible light were obtained using a Gardner colorimeter.

C_(g) values were determined as follows. The polymer (7.0 grams) wascharged to a heated mold having dimensions 5.0×0.5 inches andcompression molded at 120° C. above its glass transition temperaturewhile being subjected to applied pressure starting at 0 and ending at2000 pounds using a standard compression molding device. After therequired amount of time under these conditions the mold was allowed tocool and the molded test bar removed with the aid of a Carver press. Themolded test bar was then inspected under a polaroscope and anobservation area on the test bar located. Selection of the observationarea was based on lack of birefringence observed and sufficient distancefrom the ends or sides of the test bar. The sample was then mounted in adevice designed to apply a known amount of force vertically along thebar while the observation area of the bar was irradiated withappropriately polarized light. The bar was then subjected to six levelsof applied stress and the birefringence at each level measured with theaid of a Babinet compensator. Plotting birefringence versus stressaffords a line whose slope is equal to the stress optical coefficientC_(g).

Values of in-plane birefringence (IBR), and vertical birefringence (VBR)were measured using a Dr. Schenk Prometeus MT136E optical disk tester.The CD disks were molded, and the birefringence measurements were madeon the unmetallized, CD substrates (1.2 mm disk).

Barrel temperature is indicative of how hot the polymer is inside of themachine as you inject it into the mold and the mold temperature is thetemperature of the cavity mold that the polymer is being released into.The barrel temperature may be, for example, 350° C. and the moldtemperature may be, for example 100° C.

Examples 1-35

Listed in Table 1 are experimental glass transition temperatures(T_(g)s) for several of the blends of the present invention. In examples1-35, T_(g)s were obtained from solvent cast films. Films were preparedin the following manner. A 4 wt % concentration solution was preparedfor each of the polymers. The solutions were then combined to form theappropriate mixture. For example, for a 90/10 mixture of BCC and AMPS(Example 1), 9 g of a BCC solution was combined with 1 g of a AMPSsolution. The combined solutions were then spread onto a glass slide andthe solvent was left to evaporate overnight. The resulting films weredried for 3 days at 100° C. in a vacuum oven. Once dry, the films wereexamined for clarity and a T_(g) was measured. All of the films in Table1 were transparent, not hazy, and had a single, well defined glasstransition that could be predicted by the following mixture equation forthe T_(g) of the blend, T_(gblend):1/T _(g,blend) =w ₁ /T _(g1) +w ₂ /T _(g2)where w₁ and w₂ are the weight fractions and T_(g1) and T_(g2) are theglass transition temperatures in units of Kelvin for each of theindividual polymers of the 2-component blend.

Examples 1-5 indicate that BCC and AMPS can be mixed to form singleT_(g), transparent blends. The T_(g) of the blend is well defined by theT_(g) mixture equation given the T_(g)s of the BCC and AMPS polymers,Examples C1 and C2, respectively. Transparent, single T_(g) blends arealso indicated for Examples 6-10 for BCC/BisAP blends, Examples 11-15for BCC/PCCD blends and Examples 16-21 for BisAP/AMPS blends. The T_(g)sfor BisAP and PCCD, Examples C3 and C4, respectively, are also listed inTable 1.

TABLE 1 Examples of Polymer Blends - Film Data BCC AMPS BisAP PCCDExample [wt %] [wt %] [wt %] [wt %] PS [wt %] Tg [° C.] C1 1 141 C2 1 76C3 1 180 C4 1 70  1 0.9 0.1 121  2 0.8 0.2 118  3 0.7 0.3 111  4 0.5 0.598  5 0.3 0.7 94  6 0.9 0.1 144  7 0.8 0.2 146  8 0.6 0.4 150  9 0.4 0.6160 10 0.2 0.8 170 11 0.9 0.1 131 12 0.8 0.2 125 13 0.7 0.3 116 14 0.40.6 95 15 0.2 0.8 80 16 0.1 0.9 164 17 0.2 0.8 147 18 0.25 0.75 143 190.3 0.7 131 20 0.5 0.5 119 21 0.7 0.3 113 22 0.04 0.25 0.71 138 23 0.100.10 0.80 171 24 0.10 0.80 0.10 136 25 0.19 0.20 0.61 137 26 0.20 0.600.20 144 27 0.33 0.33 0.33 155 28 0.35 0.15 0.50 138 29 0.50 0.10 0.40137 30 0.65 0.05 0.30 139 31 0.65 0.15 0.20 130 32 0.8 0.1 0.1 126 330.75 0.2 0.05 115 34 0.1 0.8 0.1 164 35 0.2 0.75 0.05 144

Examples 22-35 also indicate transparent, single-T_(g) blends from 3components. When 3 polymers are blended together, T_(gblend) ispredicted from the weight fraction of each of the individual polymers,w₁, w₂, and w₃ and the T_(g)s of each of the individual polymers,T_(g1), T_(g2), and T_(g3) using the following mixture rule:1/T _(g,blend) =w ₁ /T _(g1) +w ₂ /T _(g2) +w ₃ /T _(g3)

Examples 22-31 demonstrate that blends of BCC, AMPS and BisAP also havewell defined T_(g)s that follow the 3-component mixture rule. Examples32 and 33, for BCC/AMPS/PS blends and Examples 34 and 35, forBisAP/AMPS/PS blends, demonstrate that polycarbonates and polystyrenecan be mixed to form transparent blends if AMPS is also included in themixture.

Examples 36-43

Select examples of the transparent polymer blends (listed in Table 2)were molded into optical articles in order to measure T_(g), C_(g),percent optical transmission, and equilibrium water uptake. Opticaltransmission at 630 nm was measured using a HP UV-Visiblespectrophotometer. The blend should have an optical transmission of atleast about 75%, more preferably at least about 80% and a C_(g) of lessthan about 60 Brewsters, more preferably less than 55 Brewsters, evenmore preferably less than 50 Brewsters. The blends were prepared bymixing dry powder from each of the individual polymer components in aHenschel high intensity mixer then molded into optical articles. C_(g)bars were either compression molded (Examples 39 and 43), or injectionmolded at temperatures between 250 and 320° C. into tensile bars(Examples 36-38 and 40-42) with “dogbone” shapes (gage section—0.125″thick; 0.500″ wide.

Examples 36 and 37 (BCC/AMPS blends) indicate that addition of AMPSdecreases the C_(g) of the blend (49 Brewsters) relative to the BCChomopolymer (52 Brewsters), while maintaining a high opticaltransmission. Similarly, Example 38 shows that the BCC/PCCD blend alsohas a high optical transmission and a C_(g) slightly decreased relativeto BCC. Examples 39 and 40, BCC/BisAP blends, also show single T_(g)sand a high transmission (Example 40), though the C_(g) is increasedrelative to BCC with the addition of BisAP. Finally, 3-component blendsare also shown in Examples 41-43 to have single Tgs and hightransmission. The BCC/AMPS/BisAP blend, Example 42, has a C_(g) of 40Brewsters, which is substantially decreased relative to BCC and BPA-PC.Most of the blends, with the notably exception of those containing alarge percentage (>about 80%) of BisAP, have lower equilibrium wateruptake than BPA-PC. It is believed that low water uptake is desirable inorder for optical disks to maintain low tilt and warpage and high datafidelity.

TABLE 2 Examples of Polymer Blends - Molded Articles BCC AMPS BisAP PCCDPS Tg Cg % T at % Water Example [wt %] [wt %] [wt %] [wt %] [wt %] [°C.] [Brewsters] 630 nm Uptake C5: BPA-PC 148 85 88 0.35 C6: BCC 1 140 5289 0.22 C7: BisAP 1 180 87 0.41 36 0.9 0.1 129 49 85 37 0.8 0.2 123 8538 0.9 0.1 134 50 84 0.26 39 0.2 0.8 170 55-60 *** 0.39 40 0.7 0.3 15253 84 0.29 41 0.65 0.15 0.2 135 53 86 0.23 42 0.2 0.2 0.6 142 40 81 0.2943 0.8 0.1 0.1 126 43 *** 0.23 ***These samples were compression moldedonly; % T not measured

Examples 44-51

The examples shown in Table 3 were prepared by mixing dry powder fromeach of the individual polymer components in a Henschel high intensitymixer and fed into a 28 mm WP extruder equipped with a mild screwdesign. The extrusion was performed using barrel temperatures from about260 to about 280° C. at a screw speed of 300 rpm and a throughput offrom about 10 to 20 lbs/hr. The resulting pellets were then injectionmolded into compact disks using an Engel 275 ton injection moldingmachine using barrel temperatures ranging from 550 to 580° F. and moldtemperatures ranging from 171 to 208° F., as shown in Table 3. Theoptical transmission at 630 nm, was greater than 88% for all the disks.Furthermore, the yellowness index (YI) and haze, both measured by aGardner colorimeter, were below 5 and 15, respectively, withinacceptable limits for CD substrates. The high transmittance and low hazeof these examples support the conclusion that the polymer blends aremiscible.

All of the blends in Examples 44-51 have substantially lower C_(g), IBRand VBR values than BPA-PC (Example C8), and most have lowerbirefringence than BCC (Example C9). As the in-plane birefringence (IBR)is at a maximum near the inner radius of these CDs and at a minimum nearthe outer radius, the range of IBR is indicated by tabulating themaximum IBR at 30 mm and the minimum IBR at 50 mm, as shown in Table 3.The difference between the maximum and minimum values gives the range ofIBR (ΔIBR). It is preferable that the maximum IBR is less than 100 nm,more preferable that it is less than 50 nm, and even more preferablethat it is less than 30 nm. Similarly, it is preferable that the minimumIBR is greater than −100 nm, more preferable that it is greater than −50nm and even more preferable that it is greater than −30 nm. Also inTable 3, are average values of vertical birefringence (VBR) calculatedby taking the arithmetic mean of VBR values at 30 and 50 mm.

TABLE 3 Examples of Polymer Blends - Molded CDs Melt Mold Percent Cg IBR[nm] IBR [nm] Avg Temp Temp Tg Trans- [Brew- Max @ Min @ IBRmax30- (VBR50, Example Composition [° F.] [° F.] [° C.] mission YI Haze sters] 30mm 50 mm IBRmin50 VBR 30)  C8 BPA-PC 570 182 142 91.1 1.4 8.4 80 34 −5994 663  C9 BCC-PC 570 182 139 88.5 4.2 10.3 50 18 −41 59 538 C10BisAP-PC 580 208 182 88.2 4.6 7.5 53.9 30 −28 58 372 C11 90/10BPA-PC/PCCD 575 182 133 89.7 2.7 10.3 73.5 17 −59 75 601 44 90/10BCC/AMPS 550 180 123 89.8 3.3 8 44.1 20 −5 25 319 45 80/20 BCC/AMPS 550180 117 88.1 4.5 9.7 35.9 13 3 9 260 46 90/10 BisAP/AMPS 580 208 14589.2 3.7 8.4 47.2 26 −36 62 255 47 90/10 BCC/PCCD 575 180 128 90.1 2.89.9 47.1 10 −4 13 472 48 80/20 BCC/PCCD 550 184 121 90.8 2.3 9.9 44.2 3−5 9 422 49 70/30 BCC/PCCD 550 171 115 91 2.1 9.5 42.4 13 −9 22 424 5076/24 BCC/BisAP 570 182 146 89.9 3.2 7.6 50.9 39 −35 74 418 51 65/20/15BCC/BISAP/AMPS 550 180 129 89.6 3 8 40.8 34 −12 47 285

Examples 44 and 45 (BCC/AMPS blends) have C_(g) values of about 44 and36 Brewsters, respectively, well below that for BCC (50 Brewsters) andBPA-PC (80). In addition, the reduced T_(g), which results in a lowermelt viscosity during molding, and the reduced C_(g), result in a lowerbirefringence in the molded CD. Example 45 has an IBR between 3 and 13nm and an average VBR of 260. It is also expected that the lower T_(g)and melt viscosity would result in improved replication for CDs andespecially for more advanced optical media with deeper pit and groovestructures such as high density DVD and DVD-recordable and rewriteableformats.

Example 46 (BisAP/AMPS) also has a much reduced VBR (about 255) relativeto BPA-PC and BCC. The IBR, though not as low as in Example 45, is stillwithin +−36 nm. Examples 47-49 (BCC/PCCD) have values of IBR within +−15nm, and average VBR values of about 420-475, well below that of BCC(538), but not quite as good as for the BCC/AMPS blends. The BCC/BisAPblend (Example 50) has a similar average VBR, but a higher IBR range(+−40 nm). Finally, the BCC/BisAP/AMPS ternary blend has an IBR rangewithin +−35 nm and an average VBR of 285, well below that of BPA-PC andBCC.

1. A miscible polymer blend selected from the group consisting of: (i) afirst polymer A, a second polymer B, a third polymer C, and an optionaladditive used in optical applications, wherein (A) is a polycarbonatecomprising structural units corresponding to structure (I)

 where R₁ and R₂ independently comprise a C₁-C₆ alkyl; X comprises CH₂;m is an integer from 4 to 7; n is an integer from 1 to 4; and p is aninteger from 1 to 4, with the proviso that at least one of R₁ or R₂ inthe 3 or 3′ position, (B) is a polymer comprising structural unitscorresponding to structure (II)

 where R₃ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy, and (C)is a polymer comprising structural units corresponding to structure(III)

 where R₄, R₅ and R₆ independently comprise a C₁-C₆ alkyl, (ii) a firstpolymer A, a second polymer B, a third polymer E, and an optionaladditive used in optical applications, wherein (A) is a polycarbonatecomprising structural units corresponding to structure (I)

 where R₁ and R₂ independently comprise a C₁-C₆ alkyl; X comprises CH₂;m is an integer from 4 to 7; n is an integer from 1 to 4; and p is aninteger from 1 to 4, with the proviso that at least one of R₁ or R₂ isin the 3 or 3′ position, (B) is a polymer comprising structural unitscorresponding to structure (II)

 where R₃ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy, and (E)is a polymer comprising structural units corresponding to structure (V)

 where R₉ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy; and (iii)a first polymer B, a second polymer C, a third polymer E, and anoptional additive used in optical applications, wherein (B) is a polymercomprising structural units corresponding to structure (II)

 where R₃ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy, (C) is apolymer comprising structural units corresponding to structure (III)

 where R₄, R₅ and R₆ independently comprise a C₁-C₆ alkyl, and (E) is apolymer comprising structural units corresponding to structure (V)

 where R₉ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy, where thepolymer blend has a glass transition temperature of from about 100° C.to about 185° C.
 2. The miscible polymer blend as defined in claim 1,wherein (A) is selected to be carbonate structural units of structure(I), the carbonate structural units of structure (I) further selectedfrom the group consisting of residues of1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane (BCC);1,1-bis(4-hydroxy-3-methylphenyl)cyclopentane;1,1-bis(4-hydroxy-3-methylphenyl)cycloheptane and mixtures thereof. 3.The miscible polymer blend as defined in claim 1, wherein (B) isselected to be vinyl polymer structural units of structure (II), thevinyl polymer structural units of structure (II) selected from residuesof α-methyl polystyrene (AMPS).
 4. The miscible polymer blend as definedin claim 1, wherein (E) is selected to be vinyl polymer structural unitsof structure (V), the vinyl polymer structural units of structure (V)selected from residues polystyrene (PS).
 5. The miscible polymer blendas defined in claim 1, wherein the first polymer (A) comprises from 1 to80 weight %, the second polymer (B) comprises from 1 to 50 weight %, andthe third polymer (C) comprises from 1 to 80 weight % of the blend. 6.The miscible polymer blend as defined in claim 1, wherein the firstpolymer (A) comprises from 50 to 98 weight %, the second polymer (B)comprises from 1 to 30 weight %, and the third polymer (E) comprisesfrom 1 to 20 weight % of the blend.
 7. The miscible polymer blend asdefined in claim 1, wherein the first polymer (B) comprises from 1 to 30weight %, the second polymer (C) comprises from 50 to 98 weight %, andthe third polymer (E) comprises from 1 to 20 weight % of the blend. 8.The miscible polymer blend as defined in claim 1, wherein the polymerblend is transparent.
 9. An article comprising the miscible polymerblend of claim
 1. 10. The article of claim 9, wherein the article is anoptical article.
 11. The article of claim 9, wherein the article is anoptical data storage medium.
 12. The article of claim 9, wherein theoptical data storage medium comprises a data layer and a transparentoverlayer adjacent to the data layer, wherein the transparent overlayerhas a thickness of equal to or less than 0.6 mm.
 13. The article ofclaim 9, wherein the optical data storage medium comprises a data layerand a transparent overlayer adjacent to the data layer, wherein the datalayer has a thickness of equal to or less than 1.1 mm and thetransparent overlayer has a thickness equal to or loss than 100 microns.14. The miscible polymer blend as defined in claim 1, wherein theoptional additive used in optical applications is from 0.0001 to 10%weight of the blend.
 15. A miscible polymer blend selected from thegroup consisting of: (i) a first polymer A, a second polymer B, a thirdpolymer C, and an optional additive used in optical applications,wherein (A) is a polycarbonate comprising structural units correspondingto structure (I)

 where R₁ and R₂ independently comprise a C₁-C₆ alkyl; X comprises CH₂;m is an integer from 4 to 7; n is an integer from 1 to 4; and p is aninteger from 1 to 4, with the proviso that at least one of R₁ or R₂ isin the 3 or 3′ position, (B) is a polymer comprising structural unitscorresponding to structure (II)

 where R₃ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy, and (C)is a polymer comprising structural units corresponding to structure

(ii) a first polymer A, a second polymer B, a third polymer E, and anoptional additive used in optical applications, wherein (A) is apolycarbonate comprising structural units corresponding to structure (I)

 where R₁ and R₂ independently comprise a C₁-C₆ alkyl; X comprises CH₂;m is an integer from 4 to 7; n is an integer from 1 to 4; and p is aninteger from 1 to 4, with the proviso that at least one of R₁ or R₂ isin the 3 or 3′ position, (B) is a polymer comprising structural unitscorresponding to structure (II)

 where R₃ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy, and (E)is a polymer comprising structural units corresponding to structure (V)

 where R₉ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy; and (iii)a first polymer B, a second polymer C, a third polymer E, and anoptional additive used in optical applications, wherein (B) is a polymercomprising structural units corresponding to structure (II)

 where R₃ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy, (C) is apolymer comprising structural units corresponding to

(E) is a polymer comprising structural units corresponding to structure(V)

 where R₉ comprises a C₁-C₆ alkyl, hydrogen, cyano or methoxy, where thepolymer blend has a glass transition temperature of from about 100° C.to about 185° C.